Ed Miliband was criticised on Monday for laying a wreath not signed in his own hand at commemorations for the centenary of the first world war – before it emerged David Cameron was the only senior guest allowed to include a personal message.

While the prime minister wrote a note about the enduring legacy of soldiers who died in the war, other guests – from Miliband to Nick Clegg and Alex Salmond – laid wreaths with only their titles printed in a large scrawl handwritten by the organisers.

Labour sources said Miliband was not given the opportunity to write a personal message as he was handed the wreath moments before he had to lay it. They said he came prepared to write a message but the procedure was different to what usually happens at the cenotaph in London and he had to take the wreath without getting the chance to sign his name.

Miliband came in for criticism from social-media users because the pictures of his wreath were the first to emerge from the service in Glasgow, which is understood to have been organised by the Department for Culture, Media and Sport.

A spokesman for the DCMS said: “The same wreaths and pre-written messages were provided to all wreath layers. Some chose to write personalised messages.”

It is understood the prime minister’s office asked for a card in advance and it was added to the wreath in the morning. No one was given time on the morning to write a message but some brought their own message or wreath and substituted it on the morning.

Despite Labour’s explanation, critics seized on pictures of the contrasting messages from Cameron and Miliband, with some comparing it to the gaffe made by Michael Foot, the former Labour leader, who was criticised for wearing a “donkey jacket” to Remembrance Sunday in 1981. It was, in fact, a short green overcoat that people compared unfavourably with his colleagues’ longer black overcoats.

Miliband has already made several contributions to the centenary commemorations, including writing a letter to an unknown soldier.

“One hundred years ago, Britain entered into the first world war and hundreds of thousands of British soldiers gave their lives to protect the freedom that we still enjoy today,” he said on Monday. “They fought valiantly and with incredible bravery in unimaginably horrific conditions.

“Young men from across Britain served alongside soldiers from across the world – from the Indian subcontinent to Africa, from Australia to the Caribbean.

“We must also remember those who served their country in other ways – from the nurses who risked their lives on the western front to those who played their part on the home front.

“The first world war will serve as a reminder of the brutality of conflict for generations to come and a reminder to those in power to avoid entering war unless it is absolutely necessary.”

• This article was updated at 3.45pm on 4 August to take in the detail that only David Cameron was allowed to include a personal message on his wreath